1. Field of the Invention
The present invention relates to a solid state imaging apparatus and a solid state photosensor arrangement and, more particularly, to those which are provided with a unique scanning section for scanning a solid state imaging device or a one-dimensional photosensitive array optical sensor.
2. Description of the Prior Art
The current trend in the art of video cameras and other imaging instrumentations is toward the use of a solid state imaging apparatus which is implemented by a solid state imaging device. A solid state imaging device which replaces the traditional image pick-up tube enhances a small-sized lightweight design of such an instrument. A predominant type of solid state imaging device known in the art is a MOS (metal oxide semiconductor) type imaging device which is easy to produce and capable of readily sensing an optical image of an object. However, the number of pixels and, therefore, resolution attainable with a MOS type imaging device is not great enough to keep up with the advent of high-grade television systems and large screens. That is, in such advanced systems, the increase in the number of pixels of the imaging device is the key to a successful display of delicate images.
As regards a solid state imaging arrangement of the type using a single imaging device, a greater number of pixels may be accomplished without resorting to any modification to the conditions of optics associated with the imaging device only if the area per pixel is reduced with the chip size unchanged. The problem with this approach is that the decrease in the area per pixel directly translates into a decrease in the light receiving area per pixel and, thereby, a decrease in the amount of light incident to each pixel. Video signals picked up from such pixels would show a prohibitively poor signal-to-noise (S/N) ratio, resulting in poor quality of images picked up by the device.
Another possible approach is increasing the chip size of an imaging device without changing the area per pixel so that the number of pixels may be increased in proportion to the increase in the total area. This approach, just as it solves the problem of the number of pixels, brings about another problem that an optical image of an object needs to be focused in greater dimensions on the imaging device complementarily to the increased chip size. That is, the optical image of an object has to be provided on the imaging device in larger magnifications relative to the object by installing a lens having a substantial focal length. Increasing the focal length of a lens without changing the f number, however, leads to an increase in the aperture of the lens which in turn results in a bulky and heavy construction of the optics and, therefore, that of the whole apparatus using such an imaging element and lens.
Another type of solid state imaging apparatus available today uses a pair of imaging devices and focuses two identical optical images of a single object to the two imaging devices through two branched optical paths. The total number of pixels attainable with the two-device type imaging apparatus is double the previously discussed single-device type imaging apparatus. In addition, the chip size can be increased to further increase the total number of pixels without substantially affecting the size and weight of the optics, because the resulting increase in the area per imaging device is only half the increase required of the imaging device of the single-device type apparatus.
Incontrovertibly, an imaging system of the kind using a pair of solid state imaging devices is apt to become rather bulky and heavy due to the use of extra optical elements such as a mirror and a prism in addition to a lens. Nevertheless, such a system is satisfactory so far as resolution is concerned and matches the current trend in the art.
The problem with the imaging system using a pair of solid state imaging elements is that the imaging apparatus focuses an image with the intermediary of a mirror. Specifically, an optical image transmitted through a dichroic mirror is focused to one imaging device in an orientation which is opposite in one direction to an optical image which is provided on the other imaging device after being reflected by the mirror. In this condition, images produced by the two imaging devices cannot be matched to each other unless they are scanned in opposite directions to each other with respect to the above-mentioned one specific direction.
Some expedients have heretofore been presented to allow a pair of imaging devices to be scanned or read in different directions for matching purpose. One of them is producing a group of imaging devices having pixels oriented in one direction and a group of imaging devices having pixels oriented in the other direction, and another is producing imaging devices each having shift registers located at both sides of a photosensitive area so that the imaging devices may be scanned in either direction. The first-mentioned expedient is undesirable because the two different kinds of imaging devices are necessarily paired in the production line keeping pace with one of the kinds which is poorer in yield than the other, at the sacrifice of economy. The second-mentioned expedient has the drawback that since one of each paired shift registers which is not faulty is used and since a fault is apt to concentrate to either one of the imaging devices in the pairs, the imaging apparatuses have to be produced, which again in pace with one of them which is poorer in yield than the other at the cost of economy.